A Japanese technology team has demonstrated ultrasonic levitation of objects that for the first time works in three dimensions. This means that as opposed to merely lifting objects with sound waves, scientists can now move them through space in every direction. (See also "Watch Sodium and Water Levitate and Collide.")

First demonstrated in the 1940s, acoustic levitation has suffered its up and downs over the years, enjoying a resurgence in the past decade brought about by more powerful electronics. Researchers have dramatized the advances by levitating such things as bees, ants, and fish.

Now, in a study submitted to the Cornell University Library's physics archive, a team led by Yoichi Ochiai of the University of Tokyo reports that they have achieved a new level of control in acoustic levitation, moving plastic beads in three dimensions with an array of 285 sound-emitting transducers as the controllers.

"It is a real advance, and it opens new possibilities for levitation," says acoustic levitation expert Rick Weber of Materials Development Inc. in Arlington Heights, Illinois.

The demonstration of three-dimensional control of acoustic levitation follows a demonstration last year by Swiss researchers of two-dimensional control, he notes, and points to rapid advances in the field.

Lattice of Sound

Beads, electronics parts, matches, screws, nuts, and alcohol droplets are just some of the things levitated by the University of Tokyo team.

In their experiment, the scientists moved beads in sweeping right-left, up-down, and backward-forward motions within their 20.5-inch-wide (520-millimeter-wide) levitation chamber.

The ultrasonic sound waves emitted by the speakers powered by the team's transducers are pitched above the range of human hearing.

By altering the strength of the sound waves emitted by the arrayed speakers in synchronized fashion, the Japanese team was able to move the beads and other objects freely, simply by the power of sound.

The array of sound-emitting transducers created a cross-shaped lattice of points in the air where sound waves combined and reinforced one another to create the lifting pressure that levitated the objects.

That means the device created a series of points in the air where beads or other objects would seem to just hang in place without any support.

Levitation Salad

The use of more transducers and a relatively simple control system run by a modern computer is what enabled the advance to three-dimensional movement, Weber says.

"With three-dimensional controls, you could combine more materials in more steps than you could previously without ever using a container," Weber says.

Ultrapure Drugs in Space

He says that testing of ultrapure pharmaceutical compounds represents the most likely application of the technology. Liquids could be analyzed while suspended in air by acoustic levitation, eliminating containers that might trigger crystallization or introduce impurities that might interfere with drug testing.

The Japanese researchers may have a different locale in mind for their technology: industrial spacecraft in orbit.

"It has not escaped our notice that our developed method for levitation under gravity suggests the possibility of developing a technology for handling objects under microgravity," they conclude at the end of their study.

The team hopes to see their technology work aboard the space station or on another spacecraft, possibly to create pharmaceuticals or ultrapure crystals via remote control, without astronauts having to be present.